This invention relates to electrophoretic information displays (EPID) in general and more particularly to apparatus which operates in conjunction with an EPID display enabling such a display to employ grey scale capability.
The prior art is replete with a number of various patents and articles concerning electrophoretic displays. Such electrophoretic displays have been widely described and disclosed in the prior art, and essentially the assignee herein, namely-Copytele, Inc. of Huntington Station, New York, has recently developed an electrophoretic display which has an image area of approximately 11.times.81/2 inches and is designed to be used either as a separate display or to be combined with other displays. The company has the ability to combine as many as four such displays to create image areas as large as approximately 22.times.17 inches.
The information on such displays can be changed either locally or remotely and can be viewed at an angle of nearly 180.degree.. Such displays have extremely high resolution and can accommodate over 160,000 pixels within an image area of approximately 2.8 inches diagonally. In regard to such displays, reference is made to U.S. Pat. No. 4,655,897 issued on Apr. 7, 1987 entitled ELECTROPHORETIC DISPLAY PANELS AND ASSOCIATED METHODS to Frank J. DiSanto and Denis A. Krusos and assigned to Copytele, Inc., the assignee herein.
In that patent there is described an electrophoretic display panel which includes a planar transparent member having disposed on a surface a plurality of vertical conductive lines to form a grid of lines in the Y direction. On top of the grid of vertical lines there is disposed a plurality of horizontal lines which are positioned above the vertical lines and insulated therefrom by a thin insulating layer at each of the intersection points. Spaced above the horizontal and vertical line pattern is a conductive plate. The space between the conductive plate and the X and Y line pattern is filled with an electrophoretic dispersion containing chargeable pigment particles.
When a voltage is impressed on the X and Y lines, pigment particles which are located in wells or depressions between the X and Y pattern are caused to migrate towards the conductive plate and are deposited on the plate in accordance with the bias supplied to the X and Y conductors.
There is described in that patent an electrophoretic dispersion suitable for operation with the display as well as techniques for fabricating the display. Hence, in this manner the displays can be fabricated to contain large effective display surfaces while being relatively thin and which are capable of high resolution and relatively low power. As indicated, the above-noted patent and others include information concerning the fabrication, operating and resolution of such displays.
In any event, it has been an extreme problem in regard to such displays to provide grey scale capability. Grey scale capability is a well known term of art and has been utilized for example in regard to the description of television receivers and various other types of data presentations such as in facsimile and so on. In the case of television receivers, the response of the receiver can be visually determined by means of typical test patterns such as those test patterns that were previously transmitted and displayed when for example a television station goes off air. Various television stations frequently transmit such a pattern for the convenience of service technicians and so on. The pattern, apart from showing correct linearity, for example the test pattern circles should appear with constant radii, permits other features to be observed. Such test patterns also show correct reproduction of the background shading which indicate proper low frequency response while correct reproduction of the five color shades in the center target area of a test pattern indicates proper mid-frequency responses. High frequency response is shown by the vertical wedges.
In any event, as one can ascertain, such test patterns are associated with grey scale capability--namely, with the display of various levels of grey as located between the shades of black and white. Such grey scale capability is a desirable feature in conjunction with any type of display. Essentially, an electrophoretic display either presents a black or a white representation of a particular image. There are no grey scale variations as the color of all graphic information presented on the display is determined by the presence or absence of pigment hence one can view such displays as being either black or white or dark or light.
It is therefore an object of the present invention to provide an electrophoretic display having grey scale capability.
It is a further object of the present invention to provide an electrophoretic display apparatus which has grey scale capability and which operates in conjunction with commercially available components to provide grey scale capability in such a display at a realistic cost and a reduced complexity.